02714 Effects of silver particles on the photovoltaic properties of dye-sensitized TiO2 thin films

02714 Effects of silver particles on the photovoltaic properties of dye-sensitized TiO2 thin films

07 Alternative energy sources (solar energy) alternative linear receivers on separate towers, This additional variable in reflector orientation provi...

225KB Sizes 0 Downloads 20 Views

07 Alternative energy sources (solar energy)

alternative linear receivers on separate towers, This additional variable in reflector orientation provides the means for much more densely packed arrays. Patterns of alternating mirror inclination can be set up such that and blocking are almost eliminated while ground coverage is maximized. Preferred designs would also use secondary optics which will reduce tower height requirements. The avoidance of large mirror row spacings and receiver heights is an important cost issue in determining the cost of ground cost, steam line preparation, array substructure cost, tower structure thermal losses and steam line cost. The improved ability to use the Fresnel approach delivers the traditional benefits of such a system, namely small reflector size, low structural cost, fixed receiver position without moving joints and non-cylindrical receiver geometry. The modelled array also uses low emittance all-glass evacuated Dewar tubes as the receiver elements. Alternative versions of the basic CLFR concept that are evaluated include absorber orientation, absorber structure, the use of secondary reflectors adjacent to the absorbers, reflector field configurations, mirror packing densities and receiver heights. A necessary requirement in this activity was the development of specific raytrace and thermal models to simulate the new concepts. 00/02707 Comparative study of the performances of four photovoltaic/thermal solar air collectors Hegazy, A. A. Energ,r Corrversion & Munugemenr, 2000, 41. (8), 861-881. An investigation of the thermal, electrical, hydraulic and overall performances of flat plate photovoltaic thermal (PVIT) air collectors has been made. Four popular designs are considered with the air flowing either over the absorber (Model I) or under it (Model II) and on both sides of the absorber in a single pass (Model III) or in a double pass fashion (Model IV). Heat balance equations are written for each model and are numerically solved, incorporating measured climate data. The effects of air specific blow rate and the selectivity of the absorber plate and PV cells on the performances have been examined. It is found that under similar operational conditions, the Model I collector has the lowest performance, while the other models exhibit comparable thermal and electrical output gains. Nevertheless, the Model III collector demands the least fan power, followed by Models IV and 11. It is also shown that selective properties are inappropriate for these PVfT collectors due to the resultant reduction in the generated PV energy, especially at low flow rates. The study provides valuable information regarding the design and operation of such types of PV/T air collectors. 00102708 Comparison between predicted and actually observed in-service degradation of a nickel pigmented anodized aluminium absorber coating for solar DHW systems Carlsson, B. Solar Energ.r Mareria1.r & Solar Cells. 2000. 61, (3). 223-238. The actual service degradation in optical performance of a nickel pigmented anodized aluminium absorber coating has been investigated in order to better validate predicted service life data from accelerated life testing. Samples from the coating taken from collectors used in solar DHW systems for time periods of 10 years or more were analysed for that purpose. The study, which was performed by the IEA Working Group: Materials in Solar Thermal Collectors, utilized results from a comprehensive joint case study on accelerated life testing previously performed in Task X of the IEA Solar Heating and Cooling Programme. It could be concluded from the present study that the agreement between degradation data determined for the absorber samples from the DHW systems and that from accelerated life testing from the Task X study was astonishingly good both from a quantitative and a qualitative point of view. For the anodized aluminium coating the results of the present study strongly point to the fact that the design of the solar collector with respect to air-tightness is the most crucial factor in determining service life. The service life was defined as the period during which the optical performance is not less than 95% of its original value. The estimated service life is of the order of 30-40 years for the coating in an airtight solar collector with controlled ventilation of air, whereas in a non-airtight collector with essential uncontrolled ventilation of air, the corresponding life is around S-10 years. The general conclusion from the study is that the accelerated life testing method as developed by the Task X group is an efficient tool in predicting expected service life of absorber coatings and is therefore to be recommended for qualification of durability of new kinds of absorber coatings. 00102709 Computer simulation of the effect of phosphorous doping of the i-layer in a thin-film a-Si:H p-i-n solar cell Prentice, J. S. C. Solrrr &erg): Marerids & Solar CcUs. 2000, 61, (3) 287300. The simulation RAUPV2 has been used to model a thin-film a-Si:H p-i-n solar cell, fabricated at the Rand Afrikaans University. For a physically acceptable set of input parameters, the simulated J-V curve agrees very well with the empirical J-V curve, under AM 1.5 g illuminatton. The effect of boron- and phosphorous doping of the i-layer (B- and P-profiling) was studied. It was found that boron doping of the i-layer greatly reduced cell performance. On the other hand, there seemed to be an optimal phosphorous concentration in the i-layer, Pop,, for which cell performance, measured in terms of maximum power output, was a maximum. It was observed that as the P concentration in the i-layer was increased towards rate in the front of the i-layer decreased, whilst that P I the recombination in?he back part of the i-layer increased. The short-circuit current was seen to decrease under P-profilmg. It was seen that as a consequence of P-

profiling, the drift field in the back part of the i-layer was relatively insensitive to the effect of an applied voltage, for applied voltages up to about 0 55 V. 00/02710 Daylight optimization of multifunctional solar facades Vartiainen, E. Solar Energy, 2000, 68, (3), 223-235. Multifunctional solar facades consisting of a transparent window and an opaque photovoltaic section are analysed and optimized. Employing numerical daylight estimation techniques, the optimal shape, position and area of the window section is determined. Maximum yearly average daylight availability is achieved with a similarly shaped window as the facade which is placed near the centre of the facade. For non-residential buildings, the yearly average useful interior daylight illuminance does not increase significantly for windows larger than 30% of the total facade area, Considering both the artificial lighting requirement replaced by daylight through the window and the electricity produced by the PV section of the facade, the maximum electricity benefit for a south-facing facade is achieved with a window area of about 10% of the total facade area in Southern Europe (38”N) and 15% in Northern Europe (60”N). 00/02711 Design of a solar photovoltaic-powered mini cathodic protection system Mishra. P. R. S&r Energy Morerids & Sob CeNs. 2000, 61. (4), 383-391. A mini cathodic protection (CP) system based on solar photovoltaic power source has been designed and tested in the field. It is concluded that such modular systems are well suited for CP applications especially in remote and hilly terrains. Education for photovoltaics and solar energy 00102712 Wenham, S. R. Solar Progress, 1999, 20, (4). 4-5. and renewable energy (RE) industries have opened up new educational opportunities. The Australian government has established a Key Centre for Photovoltaic Engineering, embarking upon collaborative research with industry and the implementation of the world’s first undergraduate engineering degree in photovoltaics and solar energy. Effect of dust on the transmittance of low density 00/02713 polyethylene glazing in a tropical climate Mastekbayeva, G. A. and Kumar, S. Solar Energy, 2000, 68, (2), 135-141. The performance of solar systems (thermal or photovoltaic) is influenced by the ability of the glazing to transmit solar radiation to the collection surface, besides other factors, such as, incident radiation, tilt of collector, properties of materials, operating strategy, surroundings, etc. This paper discusses the influence of dust on the transmittance of a 0.2 mm-thick low-density polyethylene (LDPE) glazing used commonly in solar air heaters, The reduction in transmittance due to various dust deposition densities of Bangkok clay (size 53-75 grn) has been measured and a correlation relating the dust deposition density and the transmittance given. Experimental observations of natural dust accumulation on an inclined (15”) LDPE glazing at a tropical climatic condition during a 30-day period indicates a dust accumulation of 3.72 g/m’ and is found to reduce the global transmittance of the glazing from about 87.9% to 75.8%. 00/02714 Effects of silver particles on the photovoltaic properties of dye-sensitized TiOz thin films Wen, C. S&r Energy Marerids & Solar Cells, 2000, 61. (4) 339-351. To evaluate the possibility of using the plasmon resonance effect to enhance the efficiency of photochemical cells, cis-(SCN)zBis(2,2’-bipyridyl-4,4’dicarboxylate) ruthenium (II) dye-sensitized cells were used to measure the photoresponse of TiOz film electrodes before and after deposition of silver particles. The deposited silver particles created a film with silver islands. It was found that the photoresponse in the visible region increased as the mass-equivalent silver-island film thickness, I+,~, increased to 3.3 nm. but decreased when rAp was further increased to 6 nm. On the other hand, compared with bare Ti02 films, the photoresponse in the UV region decreased for any level of silver islands. These results suggest that under proper conditions, enhancement of the optical absorption of the dye by the silver plasmon resonance effect contributes to the photocurrent and indicates the possibility of improving the energy conversion efficiency of photoelectrochemical cells with silver-island films High performance solar heating in the Rockies 00102715 Litchtwardt, M. Solar roday, 2000, 14, (2) 3639. An innovative solar air heating technology offers an elegantly simple and cost-effective solution to the problem of heating makeup air and helps protect the environment in the bargain by avoiding the release of greenhouse gases and other pollutants. 00102718 Impurity diffusion from uncoated foreign substrates during high temperature CVD for thin-film Si solar cells Beaucarne, G. So/or Energy Marerids & Solor Cells, 2000, 61, (3), 301-309. This paper studies the diffusion of impurities from three types of foreign substrates (graphite, alumina and mullite) during thermal chemical vapour deposition (CVD) of a poly-crystalline silicon film. A rapid thermal CVD (RTCVD) system is used along with characterization techniques such as secondary ion mass spectroscopy (SIMS) and deep level transient in the case of materials like spectroscopy (DLTS). Results show that, graphite, metallic contaminants can freely diffuse out into the deposited

Fuel and Energy Abstracts

September

2000

301